Because torque wrenches, particularly those used by amature builders- as opposed to race shop pros- rarely get calibrated, lubricants used (or not as in torqued dry) may vary from specs set out by the fastener mfg, and other issues many engine builders recommend measuring the stretch of critical fasteners like rod bolts rather than relying on torque specs. As Whizbang suggests measuring the length free and after every torque/run cycle can help determine if a fastener has lost its strength. After stretching, they should return to the pre use length. If not, throw away.

Also, of course, use the best fasteners you can lay hands on- ARP and similar. Upgrade the rod bolts, quality and size if possible. Follow the MFG's recommendations for torque and stretch. If your rods use bolt and nut, if you replace them the rod ends need to be resized- which you are looking at with the clearances. All this stuff I am sure you know so apologies if my restating is an issue.

Thanks for the info. Do you know someone who can hone rod big ends? The plan is to add 0.0003 to the ID and use coated upper shells and uncoated lowers.

The weak link on these engines are the fasteners that hold them together. This fretting gets worse when the horsepower increases. I do not know how to fix the issue. I manage it by minimizing the runs down the salt to just what I need to do the job and tightening the bolts every off season. The 107 HP the engine makes now looks to be the limit until I figure out a solution to this problem.

It's common on split cases like this in both automotive and cycles to have the case halves doweled to reduce the halves from shifting and fretting once they begin to exhibit signs of these issues.

measuring the length free and after every torque/run cycle can help determine if a fastener has lost its strength

Not really--all that some residual stretch says is that the fastener has undergone a bit of plastic deformation, it says nothing about its strength. When did it “lose” its strength, before it was un-torqued, or after? If before was the original make-up adequate? Why was it OK to use in its original stretched and slightly deformed condition and not in a later application? If it was adequate the first time, why would reusing the item not be just as adequate?

It is my understanding that an over stretched bolt, usually by torqueing without measuring stretch, loses its clamping ability- and an under stretched one may come loose or otherwise fail regardless of the apparent torque used to install. And that an overstretched bolt will not return to original specs (within some minor limit) My comments came from many recommendations by engine builders. Yes on the internet. Maybe wrong. The attached recommendation by Scat says in no uncertain terms that an over stretched bolt should be discarded. So perhaps we can agree to disagree.

Triumph made two changes to the eight problem bolts around the crankshaft. The first bolts were 118.5 mm long, galvanized, and torqued to 10 Nm and then to 40Nm. They were in the bike originally. They got tossed and I made the first upgrade.

The first upgrade was to 118.5 mm anodized bolts with 10 Nm followed by 75 degrees of turn. That is what is in the bike now. They were installed with Loctite. The Loctite helps prevent loosening. It also gives more thread engagement is my feeling.

The last upgrade is to use chrome plated bolts, 120.5 mm long, with 10 Nm torque followed by 75 degrees turn. There is a late model bolt in the junk pile. The short green ones are in the bike. The plan is to upgrade to all new long bolts.

The old crank had both pistons traveling up and down together. One was firing every 360 degrees. These motors have serious vibration. The counterbalancers cancel it. They are located in the upper crankcase half. There is a lot of pushing and tugging through those crankcase bolts while the crank and balancer pull in different directions. Both pistons are being yanked from TDC and BDC at the same time.

The crank pins are 90 degrees apart on this newer crankshaft. The crank will continue to tug and push against the balancer. Only one piston is at TDC and BDC at any time. This might help fix the problem.

The bolt is a tension spring and it has to stretch under load to provide clamping force. The stretch must not be large enough to permanently deform the metal. Otherwise the bolt cannot return to its original length after stretching and it provides insufficient clamping force. The limits in the chart are likely the limits on stretch values that will not permanently deform the bolt and they include a safety factor.

The reason that I follow this thread, and the Milwaukee Midget one, is that it's always been my belief that in order to design or fix anything it helps to understand completely what is happening that shouldn't or what isn't happening that should be. These two threads in particular give me insight into the detailed investigation and study that goes on with these projects. That's why I suggested that Bo perform some experiments in keeping with his thorough and disciplined manner, to find out exactly what the issue is. He may need stronger bolts, stronger threads in the case, different torque values/procedures, or something else unidentified as of now. As with everything, until you know exactly the nature of the failure, making an appropriate fix by just changing parts is only possible with luck.

Triumph made two changes to the eight problem bolts around the crankshaft. The first bolts were 118.5 mm long, galvanized, and torqued to 10 Nm and then to 40Nm. They were in the bike originally. They got tossed and I made the first upgrade.

The first upgrade was to 118.5 mm anodized bolts with 10 Nm followed by 75 degrees of turn. That is what is in the bike now. They were installed with Loctite. The Loctite helps prevent loosening. It also gives more thread engagement is my feeling.

The last upgrade is to use chrome plated bolts, 120.5 mm long, with 10 Nm torque followed by 75 degrees turn. There is a late model bolt in the junk pile. The short green ones are in the bike. The plan is to upgrade to all new long bolts.

The old crank had both pistons traveling up and down together. One was firing every 360 degrees. These motors have serious vibration. The counterbalancers cancel it. They are located in the upper crankcase half. There is a lot of pushing and tugging through those crankcase bolts while the crank and balancer pull in different directions. Both pistons are being yanked from TDC and BDC at the same time.

It looks like Triumph has a poorly designed bolt--the more highly loaded, stretchy, part is short, between the threads and the larger shank, which presumably is larger to provide some sort of locational function. The progression from galvanize to anodize to chrome suggests they are more concerned about a possible corrosion problem than anything having to do with a bolting problem.I would be very leery about using a chrome plated bolt that doesn’t have an underlayer of some other soft material since chrome is very brittle and is typically shot full of cracks.

Regarding vibration etc. If the bolted joint has been properly designed, the preload generated by the bolting should be greater than the unbalanced forces and the bolt, therefore, is essentially in a static load situation and isolated from load variation.

Quote

The stretch must not be large enough to permanently deform the metal.

Says who? WHY? Yeah, it’s the manufacturer of the bolts. But they never drag out the stress-strain curve because that would muddy the water and undercut the “don’t (permanently) stretch the bolts!” criterion. The don’t stretch ‘em criterion is simple, conservative, in many instances overly conservative, and one easily defended by the manufacturer. But it is not the last word on effective utilization of the bolt.

(There are schools of thought that say to load the bolt well into the plastic zone--if it doesn’t break on installation--it’s good to go.)

The bolt is a tension spring and it has to stretch under load to provide clamping force. The stretch must not be large enough to permanently deform the metal. Otherwise the bolt cannot return to its original length after stretching and it provides insufficient clamping force. The limits in the chart are likely the limits on stretch values that will not permanently deform the bolt and they include a safety factor.

Bo,

This is a really complex subject, with lots of nuance regarding total load Vs fastener diameter, fastener material, serviceability, thermal loads, part re-use, and other complex issues.

Interested Observer is correct about deformation/elongation. In a nutshell, if he was not, torque to yield fasteners would not work. He is also correct about fastener manufacturers being very conservative in their recommendations. And torque to yield does work well. OEM's would not specify its' use if it did not. The basic concept is that a fastener in a "slight" yield condition is better than an "improperly" installed fastener. Fasteners, of course, MUST be replaced when servicing. Not an issue for OEM servicing, but dicey when the "quality" of the service tech is at issue. I know a "Ferrari mechanic" (self labeled) who refuses to own a torque wrench, because, he knows "how tight to make things". The engines he works on suffer from several issues . . . . . . let your imagination run wild.

And the strength of the casting, where studs and/or bolts engage, is also an important factor. Obviously, the best bolt can not compensate for any clamp load lost by engagement in a low strength casting.

F/b

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The eight big bolts near the crankshaft were installed using loctite. I am pretty sure they did not rotate counterclockwise during use. Only 15 lbs-ft was needed to remove the bolts. Much greater torque was used to install them. This indicates some deformation. Either the aluminum in the cases is deforming or the bolts are stretching.

Thanks to all of these comments, and all are taken seriously, W. Walrus has developed a rocket-scientist type testing plan. New OEM Triumph bolts will be measured to the nearest 0.0001 inch before installation. They will be installed to Triumph specifications. Little dots of fingernail polish will be put on them to see if they rotate. The bike will be run on the flats in 2018.

Post run, the engine will be torn down. The fingernail polish dots will be examined to see if the bolts loosened due to rotation. The bolts will be removed and the torque required to do this will be recorded. The bolt lengths will be measured. This will help me make some informed decisions. Doweling the cases or something else might be needed.

The standard Triumph big end shells will be installed without coatings at the desired 0.002 clearance. They will be examined to see if there are any issues. The rods might be honed out and coated shells installed if there are any problems.

Rose and me are coming up onto our 40th wedding anniversary and the race budget will be used for a trip to Italy. Deferring these issues for another year, for "research" purposes, make a lot of sense. There is a lack of both time and money in the immediate future.